Such swinging devices include an electromotor which actuates via a gear transmission a threaded spindle on which a nut reciprocates. The nut is linked to a switch shaft via an oscillating element for opening and closing the shut-off valve.
It is one object of the present invention to provide a swinging device of this kind with improved power transmission at reduced demand of space and simpler construction.
This object and others which will become apparent hereinafter are realized according to the invention by providing an oscillating crank which swings between two end positions and exerts in these positions maximum torque onto the shut-off valve.
The crank is pivoted to the nut in such a manner that from its point of articulation to the nut, it has a distance to the rotating axis about which the switch shaft is rotated during swinging of the crank which distance is at a maximum when said crank is in its end positions.
According to the invention, the switch shaft is provided with a square prolongation which projects into an elongated slot of the crank so as to provide a slidable but non-rotational linkage between the switch shaft and the crank.
The surface of the crank defining the slot is lined with a synthetic coating, as e.g. Delrin in order to reduce friction therebetween. Since the elongated slot is closed, an accurate and improved connection between the oscillating crank and the switch shaft in comparison to known swinging devices is obtained. In addition, an enclosed elongated slot prevents a tilting of the switch shaft when the crank is in its end positions.
In order to provide the reciprocation of the nut via the threaded spindle and thus of the swinging motion of the crank, limit switches are provided which are adjustably attached to a switch carrier so as to allow a modification of the stroke of the oscillating crank.
Advantageously, the crank cooperates with an indicator so that each position of the crank is indicated during swinging between its end positions.